Speed control circuit for a dc brushless motor

Abstract

A speed control circuit for a dc brushless motor includes a switch circuit and a voltage-detection circuit. The voltage-detection circuit is actuated depending upon high or low voltage of power supply to thereby cause the switch circuit to output high or low operating voltage to a driver circuit of the motor in response to changes of the voltage of the power supply. The motor is adjusted and operated at desired speeds by a rated range of input voltages according to the high or low operating voltage.

1. A speed control circuit for a dc brushless motor, wherein said speed control circuit is applied to a single phase dc brushless dc motor, comprising:
 a switch circuit including a plurality of diodes to output a high or low operating voltage to a driver circuit of the motor in response to high and low voltages input from a power supply; and  
 a voltage-detection circuit controlling the switch circuit to switch between the high or low operating voltage in response to changes in the voltage of the power supply;  
 wherein when the voltage-detection circuit senses a high voltage input from the power supply, the switch circuit is actuated to output the high operating voltage to the driver circuit and thus the motor is operated at a high speed;  
 wherein when the voltage-detection circuit senses a low voltage input from the power supply, the switch circuit is actuated to output the low operating voltage to the driver circuit and thus the motor is operated at a low speed, the low operating voltage being adjusted by the switch circuit relative to the low voltage input from the power supply.  
 
   
   
     2. The speed control circuit for a dc brushless motor as defined in  claim 1 , wherein the switch circuit further includes a first transistor and a first resistor; the voltage-detection circuit includes a second transistor; when the second transistor is saturated resulting in saturation of the first transistor, the power supply is output to the driver circuit through the first transistor so as to output the high operating voltage to the driver circuit and thus the motor is operated at the high speed; and wherein when the second transistor is cut off resulting in cutting off the first transistor, a voltage of the power supply is reduced by a resistance provided with the diodes so as to output the adjusted low operating voltage to the driver circuit and thus the motor is operated at the low speed. 
   
   
     3. The speed control circuit for a dc brushless motor as defined in  claim 2 , wherein the voltage-detection circuit further includes a second resistor and a third resistor arranged to form a voltage divider; wherein when the power supply voltage has risen above a reference voltage, the voltage divider divides the voltage of the power supply to output the high voltage level to saturate the second transistor and subsequently saturate the first transistor; and wherein when the power supply has fallen below the reference voltage, the voltage divider outputs predetermined low voltage level to cut off the second transistor and subsequently cut off the first transistor. 
   
   
     4. A speed control circuit for a dc brushless motor, wherein said speed control circuit is applied to a double phase dc brushless dc motor, comprising:
 a switch circuit including a plurality of diodes to output a high or low operating voltage to a driver circuit of the motor in response to high and low voltages input from a power supply; and  
 a voltage-detection circuit controlling the switch circuit to switch between the high or low operating voltage in response to changes in the voltage of the power supply;  
 wherein when the voltage-detection circuit senses a high voltage input from the power supply, the switch circuit is actuated to output the high operating voltage to the driver circuit and thus the motor is operated at a high speed;  
 wherein when the voltage-detection circuit senses a low voltage input from the power supply, the switch circuit is actuated to output the low operating voltage to the driver circuit and thus the motor is operated at a low speed, the low operating voltage being adjusted by the switch circuit relative to the low voltage input from the power supply.  
 
   
   
     5. The speed control circuit for a dc brushless motor as defined in  claim 4 , wherein the switch circuit further includes a transistor; the voltage-detection circuit includes a first resistor and a second resistor; wherein when the transistor is cut off, a Hall driver circuit is dropped by a resistance provided with the diodes to ground and the motor is operated at the low speed; and wherein when the transistor is saturated, the Hall driver circuit is grounded through the transistor and thus the motor is operated at the high speed. 
   
   
     6. The speed control circuit for a dc brushless motor as defined in  claim 5 , wherein the first resistor and the second resistor form a voltage divider; wherein when the power supply voltage has risen above a reference voltage, the voltage divider divides the voltage of the power supply to output a high voltage level to saturate the transistor and consequently the Hall driver circuit is grounded; and wherein when the power supply voltage has fallen below the reference voltage, the transistor is cut off and consequently the Hall driver circuit is grounded through the diodes.